This invention relates to access floor systems. Access floor systems are floor systems erected on a subfloor and have an elevated surface of floor panels supported above the subfloor by a system of supporting pedestals of a given height. The floor panels are generally of uniform size and are removable to allow access to the space between the subfloor and the elevated floor system. They have high integral strength and generally include a decorative, wear-resistant surface such as vinyl tile attached to the upper surface thereof. The panels are supported from below at their corners by pedestals of adjustable height and, in some installations, have additional supporting beams or stringers that run from pedestal to pedestal and lie under the edges of the panels.
Historically, the most common use for access floor systems has been in computer room installations. The space created between the subfloor and the access panel floor accommodates the large number of electrical connections necessary in computer installations and, in some installations, may further serve as an air plenum for air conditioning purposes. Other applications for access floor systems have existed, such as a "clean room" for use in research requiring a dust-free atmosphere. A clean room has a system to provide a vertical laminar flow of filtered air from filter banks in the ceiling to a plenum chamber formed by the access floor and subfloor. The air is generally recycled constantly from the ceiling filter banks through grates in the floor panels, and back again.
Designers and builders of commercial buildings have recently taken note of access floor systems and have realized that they may be employed in a number of applications in addition to those previously discussed. Modern construction techniques for office buildings have advanced to the point where the floors of the buildings are completely supported by interior columns and thus complete flexibility is permitted in the placement of interior walls. Electrical and telephone service must be provided, however, and conduits for these wires are generally buried in the concrete floor. Consequently the placement of electrical and telephone outlets are governed by the location of the conduits buried in the concrete floor. Much greater flexibility in the placement of outlets is possible if an access floor is installed above a subfloor having no conduits buried therein because the wires may be run under the access floor to an infinite number of locations.
Certain characteristics of access floor systems have discouraged wide scale acceptance in commercial applications other than computer flooring and the like. Most notable among them is the appearance of an access floor system. Panels covered with a hard surface such as vinyl tile generally have a trim edge running around the perimeter of the panel, and an access floor assembled with such panels has a checkerboard appearance. Although this checkerboard appearance is acceptable in a number of applications, it is considered objectionable in certain instances.
If access floor systems are to gain acceptance in office building applications, it is necessary to provide systems having carpet covered panels. Covering an entire floor system with a single piece of carpet defeats the advantages of an access floor system, i.e. ease in removal of only a portion of the floor. accordingly, it is necessary to cover each panel with an individual piece of carpet.
Commercially available carpet may be classified according to several characteristics. One is the manner in which the carpet pile is attached to the carpet backing. Woven carpet has an interlocked system of pile and backing that results in a relatively strong physical bond between pile and backing, but woven carpet is made with relatively complex manufacturing techniques and thus accounts for a relatively small proportion of the carpet market. Tufted carpet is made by pushing carpet pile through one side of a separate backing fabric and then coating the surface of the backing that will ultimately face the floor with some binding means such as adhesive. Tufted carpet is easier to manufacture than woven carpet and consequently accounts for a much greater share of the market, but the physical bond between pile and backing is relatively weak when compared to the bond in woven carpet. Needle punch carpet is manufactured by forming a nonwoven flock of fibers and then binding the flock together with yarns punched through the flock with a needle. Many of the commercially available "indoor-outdoor" carpets are produced by the needle punch method. The pile on such a carpet may be very short or relatively deep, depending on the requirements for ultimate use of the carpet.
Another classifying characteristic is type of carpet pile. Looped pile is, as its name implies, a pile formed with a continuous yarn that repeatedly passes through the backing of the carpet. A single line of pile, when viewed in a cross-sectional side view of a piece of carpet, resembles a sinusoidal curve with a high amplitude but a compressed period of repetition. A looped pile in a tufted carpet is prone to ravelling because of the relatively weak bond between pile and backing. A single loop may be grasped and tugged with sufficient force to pull an entire row of carpet pile out of the backing. A looped pile in a woven carpet, on the other hand, is locked in place and would not ravel in this manner. A cut pile carpet has a pile wherein each yarn rising from the backing terminates in a cut end rather than doubling back down to the backing to form a loop pile. Cut pile carpet may be made from a loop pile carpet that has been "shaved" on its surface to remove the uppermost portions of the loops, or may be made by inserting pre-cut lengths of pile into a backing. A tufted carpet with cut pile will not ravel like a loop pile tufted carpet, but individual piles may be pulled out of the backing with relatively little effort.
The length of the pile may also vary. Plush carpets have a relatively deep pile while carpets having a tighter or denser surface have a relatively short pile.
Employing carpet as a floor panel covering is desirable from the standpoint of expanding the market for access floor systems.
Attempts have been made to cover only the top surface of floor panels with carpet. If the carpet has a relatively short pile, the carpet fibers from adjacent panels will not intermingle in the region of the joint between the panels. Consequently, the objectionable checkerboard pattern is still visible. Additionally, if this short pile carpet is of the loop pile, tufted variety, the carpet on the panels has a tendency to ravel and the cut loops along the edge of the panel where the carpet was cut to fit the panel are of varying lengths and stick up as "stray" pile yarns.
Running this short pile carpet over the edges of the panel obviates the stray pile and ravelling problems, but, of course, the checkerboard pattern is even more detectable in an installed floor system and a greater quantity of carpet per panel is required. One advantage with such a panel, however, is that the pedestals may be adjusted with a somewhat lesser degree of precision because the slight gap created between the panels where the carpet curves over the edges makes it more difficult to visually detect slight variations in panel height. It is also possible to cover only the top surface of the panel with a short pile carpet and attach a trim edge of some material such as vinyl. Again, the checkerboard pattern is quite noticeable.
Covering only the top surface of a panel with a carpet having a deep, cut pile would be desirable from the standpoint of obscuring the joints between the panels. The pile fibers from adjacent panels blend and intermingle along the panel edges and visually obscure the joint. Additionally, the cut pile is of uniform height so no stray yarns are visible and the cut pile will not ravel. It is noted, however, that the pedestal system must be adjusted with precision or else shadow lines are evident between two panels of unequal height.
A major impediment, however, to the use of deep pile carpet on floor panels is the tendency of pile fibers from an adjacent panel to be pinched in the joint between panels when one panel has been removed and is then reinserted into place. Pile fiber pinching occurs because the pile from adjoining panels extends out past the edges of the adjoining panels and thus fibers are caught or pushed down into the joint between the panels when one panel is lowered into place. This pinched or distorted pile creates unsightly lines and bunching between the panels. This pinching problem exists with any carpet having a deep pile that tends to extend past the edge of the panel, regardless whether it is looped or cut pile, and regardless whether it is woven, tufted or needle punch carpet. The governing characteristic of the pile is its height.
Building code requirements vary from jurisdiction to jurisdiction, but most codes require that wires running underneath an access floor system must be metal shielded if the space is also being used as a plenum chamber. It has been proposed to provide metal conduits of square or rectangular cross section to run between adjacent panel rows and be supported in the level of the elevated floor. The upper surface of the conduit would then form a portion of the access floor surface. Wires shielded or insulated with a non-metallic shield could then be run in the conduit. Alternatively, the conduits could be used as air ducts or conduits for other services.
The appearance of such floor system with such conduits has been considered objectionable, however, when the panels and conduit are covered with either tile or carpet of the type that shows the joints between the elements of the floor system. Long thin strips are visible in the top surface of the floor where the conduit extends across the surface. The use of a deep pile carpet on access floor systems having such a conduit would solve this problem because the pile from adjacent panels and conduits will blend together and visually obscure the joints.